CD4 and graft versus host disease: While utilizing Tregs has been demonstrated as one of the most promising cellular therapies to prevent GvHD without compromising the GvL effect in both human patients and murine models after allo-HCT [5,6,7,8], their clinical application remains limited due to major challenges in generating sufficient numbers of Tregs and maintaining their suppressor functions ex vivo, as Tregs are a very rare population in peripheral blood, constituting approximately 10% in CD4 T cells and unstable in maintaining the expression of genes associated with immunosuppressive functions [9,10].